Variable resistance to plum pox virus and potato virus Y infection in transgenic Nicotiana plants expressing plum pox virus coat protein

Abstract

The plum pox virus (PPV) coat protein (CP) gene was transferred into three species of Nicotiana using an Agrobacterium tumefaciens based system. Transgenic Nicotiana benthamiana plants that express the PPV CP exhibited protection when inoculated with PPV plant sap. After a first stage where PPV was able to multiply in transgenic and control plants, the virus was progressively excluded from newly formed tissues and at 40 days after inoculation no PPV could be detected in the most resistant lines. This homologous resistance to PPV appears to be due both to the inhibition of viral long-distance transport and to the inhibition of viral replication. Transgenic Nicotiana clevalandii and Nicotiana tobacum cv. Xanthi expressing PPV CP exhibited partial levels of protection to infection by PPV or by potato virus Y (PVY) that were dependent on the inoculum concentration. Different interpretations of these resistance phenomena are discussed.